It is a particular problem for an engine fitted with dual mass flywheel that it is subject to resonance of the dual mass flywheel at low engine speeds in what is known as a dual mass flywheel (DMF) resonance region. This resonance is a significant issue during the run-up and shut-down of the engine and particularly when the engine has to be re-started once it has begun to shut-down, a so called ‘Change of Mind Event’ (COM) as may occur if the engine is fitted with an automatic start and stop system. The line 4 on FIG. 3 shows the possible effect of attempting a restart during the resonance region and the large fluctuations of engine speed that can occur.
During the shutdown of the engine a throttle valve is generally closed to enable fast shutdown of the engine due to the effect of the low pressure (vacuum) in the inlet manifold. However, when the engine is restarted, a high manifold pressure is required and so the throttle valve needs to be open.
A conventional restart procedure enables and/or reactivates the fuelling and spark as soon as possible after the COM and this will result in a lower than optimal torque from the engine due to the low manifold pressure and may also be attempting the restart within the resonance region of the flywheel, causing severe oscillations of engine speed and possibly the inability to accelerate the engine speed above the resonance region.
An engine with a conventional restart strategy and a conventional starter motor which cannot be engaged while the engine is still turning has to avoid the DMF resonance region due to high noise and possible damage to the DMF that can result.
A strategy described herein that is employed to prevent the occurrence of such resonance either restarts the engine before the DMF region is reached (Option 1) (Line 1 on FIGS. 3 and 1′ on FIG. 4) or waits until the engine has definitely stopped (Option 2) (Lines 2 and 3 on FIG. 3 and lines 2′ and 3′ on FIG. 4).
Option 1 is only applicable if the COM happens early in the shut-down cycle before the speed falls into the resonance region and the engine is then restarted without the use of a starter motor by providing fuel and spark to the engine in the case of an S.I. Engine and using the existing rotational speed/inertia to start the engine. This has the disadvantage that there is only a small window of opportunity to employ such a technique and so generally Option 2 described below may be used for the majority of restarts.
In the case of Option 2 the engine has to completely stop as indicated by Line 2 before it can be restarted. This is because a conventional starter motor cannot be engaged with a moving flywheel without causing damage. Once the engine has stopped the starter motor is engaged to restart the engine (Line 3 on FIG. 3). This approach adds considerable time to the COM and is likely to lead to customer dissatisfaction due to long restart times. In addition, it increase wear of the starter motor and reduces fuel economy due to the need to recharge the battery used to power the starter motor more frequently.
It is an object of this description to provide an improved method for dealing with a Change of Mind Event during the shut-down and restart of an engine. It is a second object to overcome resonance of a dual mass flywheel.
According to a first aspect of the description there is provided a method for controlling an engine following an automatic engine shut-down request comprising determining whether a change of mind has occurred and, if a change of mind has occurred, preventing the restarting of the engine if the rotational speed of the engine is within a predetermined speed range in which resonance of an engine related component occurs.
The engine may have a dual mass flywheel and the engine related component may be the dual mass flywheel. The method may further comprise restarting the engine when the engine speed falls below the predetermined speed range. The method may further comprise preparing the engine for the restart while it is in the predetermined speed range. Preparing for the restart may comprise opening a throttle valve of the engine so as to admit air to the engine. Preparing for the restart may comprise reducing from a normal level to a lower level, one or more auxiliary load applied to the engine. The or each auxiliary load may be a load from an accessory device driven by the engine. The method may further comprise returning to the normal level the or each auxiliary load after the engine speed has risen to a speed above the predetermined speed range following the restart of the engine.
According to a second aspect of the description there is provided a system for controlling the operation of an engine following an automatic shut-down request wherein the system includes an electronic control unit arranged in response to the automatic engine shut-down request to shut-down the engine, determine whether a change of mind has occurred and, if a change of mind has occurred, prevent the restarting of the engine if the rotational speed of the engine is within a predetermined speed range in which resonance of at least one engine related component occurs.
The engine may have a dual mass flywheel and the at least one engine related component may be the dual mass flywheel. The electronic control unit may be further arranged to restart the engine when the engine speed falls below the predetermined speed range. The electronic control unit may be further operable to prepare the engine for the restart while the speed of the engine is in the predetermined speed range. The system may further include a throttle valve controlled by the electronic control unit and the electronic control unit may prepare for the restart by opening the throttle valve of the engine so as to admit air to the engine. The electronic control unit may prepare for the restart by reducing from a normal level to a lower level, one or more auxiliary load applied to the engine. The or each auxiliary load may be a load from an accessory device driven by the engine. The electronic control unit may be further operable to return to the normal level the or each auxiliary load after the engine speed has risen to a speed above the predetermined speed range following the restart.
According to a third aspect of the description there is provided a motor vehicle having a system for controlling the operation of an engine following an automatic shut-down request constructed in accordance with said second aspect of the description.
The present description may provide several advantages. Specifically, the approach may reduce engine noise and vibration. Additionally, the approach may reduce engine emissions by limiting engine restarting to conditions that are suitable for lower emission restarts.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.